Valve units usually have a valve member by means of which a cross-section of a gas flow-conveying channel through which a fluid can flow can be changed. For this, the valve member can be actuated discontinuously to be able to adjust it between discrete switching positions. Once such discrete switching positions are reached, the valve member has to be stopped. In order to be transferred into another switching position, the valve member has to be appropriately accelerated. In case of short switching times and/or short time intervals between successive switching operations, a comparatively high amount of energy for decelerating and accelerating the valve member is necessary. A drive device which is suitable for this has a comparatively complicated structure and, accordingly, can be expensive.
Alternatively, such a valve member can also be actuated continuously. For example, the valve member rotates about an axis and runs through different switching states with each rotation. Such a valve member can be permanently driven. By varying the rotational speed, different switching frequencies or switching times can be implemented.
A valve unit of the aforementioned type can be used in a motor vehicle for adjusting the exhaust gas recirculation rate. For this purpose, the associated valve member can be arranged in a fresh air path of the internal combustion engine so that, by periodically opening and closing the cross-section through which a fluid can flow, pressure oscillations are generated or amplified by means of which the exhaust gas recirculation rate can be adjusted. By the pressure oscillations generated by means of the valve unit in the fresh air path, among other things, oscillation phases with a comparatively low pressure are generated which allow or facilitate that exhaust gas can flow over from a recirculation line into a fresh air path. Thereby, it is in particular also possible to achieve an exhaust gas recirculation on the pressure side of a charging device in a supercharged internal combustion engine.
Additionally or alternatively, such a valve unit can also be arranged in a recirculation line in order to generate or amplify pressure oscillations by periodically opening and closing the cross-section through which a fluid can flow by means of the valve member. Said pressure oscillations have oscillation phases with a relatively high pressure which allow or facilitate that the exhaust gas flows over from the recirculation line into a fresh gas path. Here too, the use in a supercharged internal combustion engine can be implemented, wherein the recirculated exhaust gas is conveyed into the high pressure side of the fresh air path.